The effect of particulate material and the loading of bacteria on a high dose PAC-MF system

Abstract

The effects of particulate material, their size distribution and the loading of total bacteria based on the age distribution of powdered activated carbon (PAC) were investigated in a hybrid membrane process consisting of an immersed microfiltration membrane system in a completely aerated reactor containing high concentration (40 g/L) of PAC. The laboratory-scale experiments on PAC-MF system were carried out using actual surface water (Tama River, Tokyo), before and after the treatment by a biofilter media. As a result of continuous filtration and backwash experiments, improvement of filtrate water quality and controls of membrane fouling were demonstrated by the addition of PAC. 52% of the PAC fell into a particle size between 22 μm and 45 μm. PAC larger than 125 μm and smaller than 22 mm were 6% and 4% respectively. Due to continuous aeration and Brownian motion of the particles, the size of the PAC inside the reactor was becoming smaller day by day. After 162 days of operation, the particle size from 1-10 μm was higher, which is the suitable size range for the adsorption of bacteria. At the same time, the number of total bacteria was also increasing inside the reactors. The membranes were fouled shortly during end of the operation due to the heavy load of fine particles and high accumulation of bacteria. However, PAC acts as an adsorbent media inside the reactors that causes successive accumulation of total bacteria.